1. Field of the Invention
The present invention relates to a wireless communication receiving device and a wireless communication system, which are applied to, for example, a sphere decoder or the like of a communication equipment using space division multiplexing in the case of a closest approach point of a lattice code (SDM code) in information communication.
2. Description of the Related Art
Heretofore, for example, a search algorithm for a communication equipment using space division multiplexing in the case of a closest approach point of a lattice code in information communication is disclosed. These techniques are described in the following Document 1, Document 2, and the like. Description will be given by taking Document 1 and Document 2 as an example.
1. Document 1
A universal lattice code decoder for fading channels Viterbo, E.; Bouros, J.; Information Theory, IEEE Transactions on, Volume: 45, Issue: 5, Jul. 1999 Pages: 1639-1642
A sphere decoder shown in, for example, in FIG. 2 of Document 1, is of a tree search algorithm for narrowing down the solution candidate points while narrowing the search area. According to this search algorithm, the solution candidate points are narrowed down while the search area is narrowed down, and hence decoding accuracy substantially equal to maximum likelihood determination can be achieved by a very small calculation amount as compared with total solution search.
However, this search algorithm is a complicated tree search algorithm requiring a large number of comparison determination steps, and hence control is complicated, and the operation range increases or decreases depending on the comparison determination step, and the operation range therefore varies. For this reason, the processing time of the decoding operation has a tendency to become unable to be made constant.
Furthermore, since it is a complicated tree search algorithm that requires a large number of comparison determination steps, the control is complicated, and hence pipeline processing of the decoding operation also tends to be unable to be performed.
Moreover, the conventional receiving device is not suited to realtime processing, and a dedicated circuit or the like is required, and hence the circuit size is increased and power consumption is also increased.
For example, in this algorithm, when a reception signal is input in synchronization with a 20 MHz clock, even if decoding can be completed within 10 clock pulses on the average, or within 20 clock pulses in the worst case, the operation must be performed at 400 MHz so as to perform realtime processing for the worst case. Further, while the tree search is performed, decoding processing for the next signal cannot be performed, and hence a contrivance for preparation of a buffer for reception signal, and a contrivance for preparation of plural processing systems are required.
2. Document 2
A new reduced-complexity sphere decoder for multiple antenna systems Chan, A. M.; Inkyu Lee; Communications, 2002. ICC 2002. IEEE International Conference on, Volume: 1, 28 Apr.-2 May 2002 Pages: 460-464
A method of reducing a calculation amount is also shown in FIG. 1 of this Document 2. However, this search algorithm is also a tree search algorithm, and hence the same tendency as described above exists.
As described above, in the conventional wireless communication receiving devices, the processing time of the decoding operation has a tendency to become unable to be made constant.